* The current update is based on an enhanced methodology implemented in March 2011

1/ The FHWA estimates national trends by using State reported Highway Performance and Monitoring System (HPMS) data, fuel consumption data (MF-21 and MF-27), vehicle registration data (MV-1, MV-9, and MV-10), other data such as the R. L. Polk vehicle data, and a host of modeling techniques. Starting with the 2009 VM-1, an enhanced methodology is used to provide timely indictors on both travel and travel behavior changes.

3/ Single-Unit – single frame trucks that have 2-Axles and at least 6 tires or a gross vehicle weight rating exceeding 10,000 lbs.

4/ Vehicle occupancy is estimated by the FHWA from the 2001 National Household Travel Survey (NHTS); For single unit truck and heavy trucks, 1 motor vehicle miles travelled = 1 person-miles traveled.

5/ VMT data are based on the latest HPMS data available; it may not match previous published results.

The data now on the website for 2000-2006 were estimated using a methodology developed in the late 1990s. FHWA recently developed a new methodology and used it for this year's Highway Statistics. This methodology takes advantage of additional and improved information available beginning in 2007 when states were first required to report motorcycle data – before that time, the reporting was not mandatory and the data were missing for a few states. Also, the new methodology does not rely on data from the national vehicle inventory and use survey which provided critical data for the original methodology but was not collected in 2007 as planned.

In April 2011, FHWA recalculated the 2000-2008 data along with the 2009 data to estimate trends. However, after further review and consideration, the agency determined that it is more reliable to retain the original 2000-2006 estimates because the information available for those years does not fully meet the requirements of the new methodology. Thus, the original 2000-2006 estimates are now used, whereas the 2007-2009 data are still based on the new methodology.